Device and method for lithography

ABSTRACT

Apparatus and method for transferring a pattern from a template ( 10 ) having a structured surface to a substrate ( 12 ) carrying a surface layer of a radiation polymerisable fluid ( 14 ). The apparatus comprises a first main part ( 101 ) and a second main part ( 102 ) having opposing surfaces ( 104;105 ), means for adjusting a spacing ( 115 ) between said main parts, support means ( 106 ) for supporting said template and substrate in mutual parallel engagement in said spacing with said structured surface facing said surface layer, a radiation source ( 110 ) devised to emit radiation into said spacing. A cavity ( 115 ) has a first wall comprising a flexible membrane ( 113 ) devised to engage said template or substrate, and means ( 114;116 ) are provided for applying an adjustable overpressure to a medium present in said cavity, whereby an even distribution of force is obtained over the whole of the contact surface between the substrate and the template. The apparatus further includes a heater device having a surface facing said spacing, for heating either fluid layer ( 14 ).

FIELD OF THE INVENTION

The invention relates to a device in connection with the lithography ofstructures on a micro or nanometre scale. In particular, the inventionrelates to imprint lithography on substrates or objects.

BACKGROUND

The trend in microelectronics, as well as in micromechanics, is towardsever smaller dimensions. Some of the most interesting techniques forfabrication of micro and submicro structures include different types oflithography.

Photolithography typically involves the steps of coating a substratewith a photoresist material to form a resist layer on a surface of thesubstrate. The resist layer is then exposed to radiation at selectiveportions, preferably by using a mask. Subsequent developing steps removeportions of the resist, thereby forming a pattern in the resistcorresponding to the mask. The removal of resist portions exposes thesubstrate surface, which may be processed by e.g. etching, doping, ormetallisation. For fine scale replication, photolithography is limitedby diffraction, which is dependent on the wavelength of the radiationused. For fabrication of structures on a scale of less than 50 nm, sucha short wavelength is needed that the material requirements on theoptical systems will be major.

An alternative technique is imprint technology. In an imprintlithography process, a substrate to be patterned is covered by amouldable layer. A pattern to be transferred to the substrate ispredefined in three dimensions on a stamp or template. The stamp isbrought into contact with the mouldable layer, and the layer issoftened, preferably by heating. The stamp is then pressed into thesoftened layer, thereby making an imprint of the stamp pattern in themouldable layer. The layer is cooled down until it hardens to asatisfactory degree followed by detachment and removal of the stamp.Subsequent etching may be employed to replicate the stamp pattern in thesubstrate. The steps of heating and cooling the combined stamp andsubstrate can bring about movement in the engaging surfaces due to heatexpansion. The larger the area to be imprinted, the larger the actualexpansion and contraction, which can make the imprint process moredifficult for larger surface areas.

A different form of imprint technology, generally known as step andflash imprint lithography has been proposed by Willson et al. in U.S.Pat. No. 6,334,960, and also by Mancini et al in U.S. Pat. No.6,387,787. Similar to the imprint technique briefly described above,this technique involves a template having a structured surface defininga pattern to be transferred to a substrate. The substrate is covered bya layer of polymerisable fluid, into which layer the template is pressedsuch that the fluid fills recesses in the pattern structure. Thetemplate is made from a material which is transparent to a radiationwavelength range which is usable for polymerising the polymerisablefluid, typically UV light. By applying radiation to the fluid throughthe template, the fluid is solidified. The template is subsequentlyremoved, after which the pattern thereof is replicated in the solidpolymer material layer made from the polymerised fluid. Furtherprocessing transfers the structure in the solid polymer material layerto the substrate.

WO 02/067055 to Board of Regents, the University of Texas System,discloses a system for applying step and flash imprint lithography.Among other things, this document relates to production-scaleimplementation of a step and flash apparatus, also called a stepper. Thetemplate used in such an apparatus has a rigid body of transparentmaterial, typically quartz. The template is supported in the stepper byflexure members, which allow the template to pivot about both X and Yaxes, which are mutually perpendicular in a plane parallel to thesubstrate surface to be imprinted. This mechanism also involves a piezoactuator for controlling parallelism and the gap between the templateand the substrate. Such a system is, however, not capable of handlinglarge area substrate surfaces in a single imprint step. A step and flashsystem offered on the market is the IMPRIO 100, provided by MolecularImprints, Inc, 1807-C West Braker Lane, Austin, Tex. 78758, U.S.A. Thissystem has a template image area of 25×25 mm, and a street width of 0.1mm. Although this system is capable of handling substrate wafers of upto 8 inches, the imprint process has to be repeated by lifting thetemplate, moving it sideways, and lowering it to the substrate again, bymeans of an X-Y translation stage. Furthermore, for each such step,renewed alignment as well as new deposition of polymerisable fluid hasto be performed. This technique is therefore very time-consuming, andless than optimum for large scale production. Furthermore, besidesproblems of repeated alignment errors, and high accuracy demands on thetranslation stage, this technique suffers from the drawback thatcontinuous structures which are larger than said template size cannot beproduced. All in all, this means the productions costs may be too highto make this technique interesting for large scale production of finestructure devices.

SUMMARY OF THE INVENTION

Accordingly, an object of the present invention is to provide methodsand means for improving fabrication of structures comprisingthree-dimensional features on a micro or nanometre scale. In particular,it is an object to provide improved methods and means for transferring apattern of such structures to substrates having widths of more than oneinch, and even for 8 inch diameters, 12 inch diameters, and larger. Anaspect of this object is to provide an apparatus and an associatedprocess which is more cost effective and more versatile.

According to a first aspect, this object is fulfilled by an apparatusfor transferring a pattern from a template having a structured surfaceto a substrate carrying a surface layer of a radiation polymerisablefluid, said apparatus comprising a first main part and a second mainpart having opposing surfaces, means for adjusting a spacing betweensaid main parts, support means for supporting said template andsubstrate in mutual parallel engagement in said spacing with saidstructured surface facing said surface layer, a radiation source devisedto emit radiation into said spacing, a cavity having a first wallcomprising a flexible membrane devised to engage said template orsubstrate, means for applying an adjustable overpressure to a mediumpresent in said cavity, and a heater device having a surface facing saidspacing. Due to the flexible membrane, an absolutely even distributionof force is obtained over the whole of the contact surface between thesubstrate and the template, whereby patterning of large area substratesin a single imprint step is made possible.

Preferably, said radiation source is positioned in said first main part,devised to emit radiation into said spacing from a first direction, andsaid heater device is positioned in said second main part, having saidsurface of the heater device facing said spacing from a seconddirection, opposite said first direction.

In one embodiment, said heater device comprises a heating element,connected to an energy source.

In one embodiment, said heater device comprises a cooling element,connected to a cooling source.

Preferably, said medium comprises a gas or a liquid.

In one embodiment, said medium comprises air.

In one embodiment, said means for applying an adjustable overpressure isarranged to adjust the pressure to 1-500 bar.

Preferably, said cavity is defined by a part of the surface of saidfirst main part, a flexible seal member arranged in and protruding fromsaid first main part surface, and said membrane which engages said sealmember.

In a preferred embodiment, said membrane is disconnectable from saidseal member, and devised to engage said seal member by application ofpressure from said second main part.

Preferably, said membrane is transparent to a wavelength range of saidradiation, said radiation source being positioned behind said membrane.

In one embodiment, said membrane and at least a portion of said surfaceof said first main part is transparent to a wavelength range of saidradiation, said radiation source being positioned behind said portion ofsaid surface of said first main part.

In a preferred embodiment, said portion of said surface of said firstmain part is made from quartz, calcium fluoride or any other pressurestable material being transparent to said radiation.

Preferably, said radiation source is devised to emit radiation at leastin a wavelength range of 100-500 nm.

In a preferred embodiment, said radiation source is air-cooled anddevised to emit pulsating radiation with a pulse duration of 0.5-10 μsand a pulse rate of 1-10 pulses per second.

In one embodiment, said membrane consists of a polymer material.

In a preferred embodiment, said membrane has a diameter or width of50-1000 mm.

In one embodiment, said substrate acts as said membrane.

According to a second aspect, the object of the present invention isfulfilled by a method for transferring a pattern from a template havinga structured surface to a substrate carrying a surface layer of aradiation polymerisable fluid, comprising the steps of:

arranging said template and substrate mutually parallel in an imprintapparatus, with said structured surface facing said surface layer,between a stop member and a first side of a flexible membrane;

heating said surface layer by means of a heater device in said imprintapparatus;

applying an overpressure to a medium present on a second side of themembrane, opposite to said first side, for imprinting said pattern intosaid layer; and

exposing said layer to radiation for solidifying said layer.

In a preferred embodiment, the method further comprises the step of:

baking said layer by providing heat from said heater device after saidstep of exposing said layer to radiation.

Preferably, said medium comprises a gas or a liquid.

In one embodiment, said medium comprises air.

Preferably, the method comprises the step of:

placing said membrane in direct engagement with said template or saidsubstrate.

In a preferred embodiment, the method comprises the step of:

clamping said membrane at a peripheral portion thereof between said stopmember and a seal member, thereby defining a peripheral wall for acavity for said medium.

Preferably, the method comprises the steps of:

emitting radiation to said layer through said template, which templateis transparent to a wavelength range of a radiation usable forpolymerising said fluid; and

heating said substrate by direct contact with said heater device.

Alternatively, the method may comprise the steps of:

emitting radiation to said layer through said substrate, which substrateis transparent to a wavelength range of a radiation usable forpolymerising said fluid; and

heating said template by direct contact with said heater device.

In a preferred embodiment, the method comprises the step of:

emitting radiation to said layer through said membrane, which membraneis transparent to a wavelength range of a radiation usable forpolymerising said fluid.

Preferably, the method comprises the step of:

emitting radiation to said layer through said membrane, and through atransparent wall opposing said membrane, defining a back wall for acavity for said medium, which back wall and membrane are transparent toa wavelength range of a radiation usable for polymerising said fluid.

In one embodiment, the step of exposing said layer comprises the stepof:

emitting radiation from a radiation source within a wavelength range of100-500 nm.

In a preferred embodiment, the method comprises the steps of:

air-cooling said radiation source, and emitting pulsating radiation witha pulse duration in the range of 0.5-10 μs and a pulse rate in the rangeof 1-10 pulses per second.

In one embodiment, the method comprises the step of:

using said substrate as said membrane.

In another embodiment, the method comprises the step of:

clamping said substrate and template together prior to arranging saidtemplate and substrate between said stop member and said flexiblemembrane.

In yet another embodiment, the method comprises the step of:

applying a vacuum between said template and said substrate in order toextract air inclusions from said surface layer prior to exposing saidlayer to radiation.

According to a third aspect, the object of the present invention isfulfilled by a method for transferring a pattern from a template havinga structured surface to a substrate carrying a surface layer of aradiation polymerisable fluid, wherein said template includesprotrusions defining a pattern, which protrusions have non-transparentlayers at outer ends, comprising the steps of:

arranging said template and substrate mutually parallel in an imprintapparatus, with said structured surface facing said surface layer,between a stop member and a first side of a flexible membrane;

heating said surface layer by means of a heater device in said imprintapparatus;

applying an overpressure to a medium present on a second side of themembrane, opposite to said first side, for imprinting said pattern intosaid layer; and

exposing said layer to radiation for solidifying said layer at portionsbetween said protrusions.

In a preferred embodiment, the method further comprises the step of:

baking said layer by providing heat from said heater device after saidstep of exposing said layer to radiation.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described in greater detail below with referenceto the accompanying drawings, on which:

FIGS. 1-3 schematically illustrate the main process steps fortransferring a pattern from a template to a substrate, wherein radiationis applied through a transparent template to solidify a polymerisablefluid on the substrate surface;

FIGS. 4-6 schematically illustrate corresponding process steps fortransferring a pattern from a template to a substrate, wherein radiationis applied through a transparent substrate to solidify a polymerisablefluid on the substrate surface;

FIG. 7 schematically illustrates an embodiment of an apparatus accordingto the invention, for performing the process as generally described inFIG. 1-3 or 4-6;

FIG. 8 schematically illustrates the apparatus of FIG. 7, when loadedwith a template and a substrate at an initial step of the process;

FIG. 9 illustrates the apparatus of FIGS. 7 and 8, at an active processstep of transferring a pattern from the template to the substrate; and

FIGS. 10-12 illustrates an alternative embodiment of an imprint processaccording to the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The present invention relates, in general, to a method of transferring apattern from a template to a substrate, by creating a relief image of astructure on a surface of the template on a surface of the substrate.The surface of the template and the surface of the substrate are in thisprocess arranged generally parallel to each other, and the transfer ofthe pattern is obtained by pressing the structured template surface intoa formable layer disposed on the substrate surface. The formable layeris treated to solidify, such that its shape is forced to resemble thetemplate surface. The template can thereafter be removed from thesubstrate and its layer, said layer now being an inverted topographicalreplica of the template. In order to permanent the transferred patternin the substrate, further processing may be required. Typically, wet ordry etching is performed to selectively etch the surface of thesubstrate under the solidified layer, whereby the pattern in thesolidified layer is transferred to the substrate surface. This much isstate of the art, and is well described in prior art documents, such asthe aforementioned U.S. Pat. No. 6,334,960.

FIGS. 1-3 schematically present the basic process steps of the actualpattern transfer steps, or imprint steps, of an embodiment of theinvention.

In FIG. 1 a template 10 is illustrated, the template having a structuredsurface 11, in which three-dimensional protrusions and recesses areformed with a feature size in height and width within a range of 1 nm toseveral μm, and potentially both smaller and larger. The thickness oftemplate 10 is typically between 10 and 1000 μm. A substrate 12 has asurface 17 which is arranged substantially parallel to template surface11, with an intermediate spacing between the surfaces at the initialstage shown in FIG. 1. The substrate 12 comprises a substrate base 13,to which the pattern of template surface 11 is to be transferred. Thoughnot shown, the substrate may also include a support layer below thesubstrate base 13. In a process where the pattern of template 10 is tobe transferred to substrate 12 directly through an imprint in apolymerisable fluid, said fluid may be applied as a surface layer 14directly onto the substrate base surface 17. In alternative embodiments,indicated by the dashed line, a transfer layer 15 is also employed, ofe.g. a polymer. Examples of such, and how they are used in thesubsequent process of transferring the imprinted pattern to thesubstrate base 13, are also described in U.S. Pat. No. 6,334,960. In anembodiment including a transfer layer 15, substrate surface 17 denotesthe upper or outer surface of the transfer layer 15, which in turn isarranged on the substrate base surface 18.

Substrate 12 is positioned on a heater device 20. Heater device 20preferably comprises a heater body 21 of metal, e.g. aluminium. A heaterelement 22 is connected to or included in heater body 21, fortransferring thermal energy to heater body 21. In one embodiment, heaterelement 22 is an electrical immersion heater inserted in a socket inheater body 21. In another embodiment, an electrical heating coil isprovided inside heater body 21, or attached to a lower surface of heaterbody 21. In yet another embodiment, heating element 22 is a formedchannel in heater body 21, for passing a heating fluid through saidchannel. Heater element 22 is further provided with connectors 23 forconnection to an external energy source (not shown). In the case ofelectrical heating, connectors 23 are preferably galvanic contacts forconnection to a current source. For an embodiment with formed channelsfor passing a heating fluid, said connectors 23 are preferably conduitsfor attachment to a heated fluid source. The heating fluid may e.g. bewater, or an oil.

Heater body 21 is preferably a piece of cast metal, such as aluminium,stainless steel, or other metal. Furthermore, a body 21 of a certainmass and thickness is preferably used such that an even distribution ofheat at an upper side of heater device 20 is achieved, which upper sideis connected to substrate 12 for transferring heat from body 21 throughsubstrate 12 to heat layer 14. For an imprint process used to imprint2.5″ substrates, a heater body 21 of at least 2.5″ diameter, andpreferably 3″ or more, is used, with a thickness of at least 1 cm,preferably at least 2 or 3 cm. For an imprint process used to imprint 6″substrates, a heater body. 21 of at least 6″ diameter, and preferably 7″or more, is used, with a thickness of at least 2 cm, preferably at least3 or 4 cm. Heater device 20 is preferably capable of heating heater body21 to a temperature of 200-300° C., though lower temperatures will besufficient for most processes.

For the purpose of providing controlled cooling of layer 14, heaterdevice 20 is further provided with a cooling element 24 connected to orincluded in heater body 21, for transferring thermal energy from heaterbody 21. In a preferred embodiment, cooling element 24 comprises aformed channel or channels in heater body 21, for passing a coolingfluid through said channel or channels. Cooling element 24 is furtherprovided with connectors 25 for connection to an external cooling source(not shown). Preferably, said connectors 25 are conduits for attachmentto a cooling fluid source. Said cooling fluid is preferably water, butmay alternatively be an oil, e.g. an insulating oil, or any othersuitable coolant.

Examples of available and usable polymerisable or curable fluids forlayer 14 comprise NIP-K17 and NIP-K22 from ZEN Photonics, 104-11 Moonji-Dong, Yusong-Gu, Daejeon 305-308, South Korea. NIP-K17 has a maincomponent of acrylate, and has a viscosity at 25° C. of about 9.63 cps.NIP-K22 also has a main component of acrylate, and a viscosity at 25° C.of about 5.85 cps. Both substances are devised to cure under exposure toultraviolet radiation above 12 mW/cm² for 2 minutes.

Another example of an available and usable polymerisable fluid for layer14 is Ormocore from Micro Resist Technology GmbH, Koepenicker Strasse325, Haus 211, D-12555 Berlin, Germany. This substance has a compositionof inorganic-organic hybrid polymer, unsaturated, with a 1-3%photopolymerisation initiator. Viscosity is 3-8 mPas at 25° C., and thefluid may be cured under exposure of radiation with 500 mJ/cm² at awavelength of 365 nm. Other examples of polymerisable materials arementioned in U.S. Pat. No. 6,334,960.

The thickness of layer 14 when deposited on the substrate surface istypically 10 nm-10 μm, depending on application area. The polymerisablefluid may be applied by spin coating, roller coating, dip coating orsimilar. A typical advantage with the present invention, compared to theprior art step and flash method, is that the polymer fluid may be spincoated on the entire substrate, which is an advantageous and fastprocess. The step and flash method, on the other hand, has to userepeated dispensation by dripping on repeated surface portions, sincethat method is incapable of handling large surfaces in single steps.

The arrows of FIG. 1 illustrate that the template surface 11 is pressedinto surface 16 of the polymerisable fluid layer 14. At this step,heater device 20 is preferably used to control the temperature of layer14, for obtaining a suitable viscosity in the material of layer 14.

FIG. 2 illustrates how the structures of template surface 11 has made animprint in the fluid layer 14, at which the fluid has been forced tofill the recesses in template surface 11. In the illustrated embodiment,the highest protrusions in template surface 11 do not penetrate all theway down to substrate surface 17. This may be beneficial for protectingthe substrate surface 17, and particularly the template surface 11, fromdamage. However, in alternative embodiments, such as one including atransfer layer, imprint may be performed all the way down to transferlayer surface 17. In the embodiment illustrated in FIGS. 1-3, thetemplate is made from a material which is transparent to radiation 19 ofa predetermined wavelength or wavelength range, which is usable forsolidifying a selected polymerisable fluid. Such materials may e.g. bequartz or various forms of polymers, dependent on the radiationwavelength. Radiation 19 is typically applied when template 10 has beenpressed into fluid layer 14 with a suitable alignment between template10 and substrate 12. When exposed to this radiation 19, solidificationof the polymerisable fluid is initiated, for solidification to a solidbody 14′ taking the shape determined by the template 10. However, heaterdevice 20 is preferably used to provide heat to layer 14′, for bakinglayer 14′ to a solid body before separation of template 10 and substrate12.

The template 10 is thereafter removed, e.g. by a peeling and pullingprocess. The formed and solidified polymer layer 14′ remains on thesubstrate 12. The various different ways of further processing of thesubstrate and its layer 14′ will not be dealt with here in any detail,since the invention as such is neither related to such furtherprocessing, nor is it dependent on how such further processing isachieved.

FIGS. 4-6 schematically present the basic process steps of the actualpattern transfer steps, or imprint steps, of an alternative embodimentof the invention. The only real difference from the embodiment of FIGS.1-3 is that in this embodiment the radiation 19 is applied throughsubstrate 12 instead of through template 10, while the same referencemarks have been used. Furthermore, heater device 20 is instead connectedto template 10, for heating layer 14 through template 10. Heater device20 of FIGS. 4-6 otherwise comprises the same features as the heaterdevice of FIGS. 1-3, wherefore the same reference markings have beenused. No further explanation of the features of FIGS. 4-6 will thereforebe made.

FIG. 7 schematically illustrates a preferred embodiment of an apparatusaccording to the present invention, also usable for carrying out anembodiment of the method according to the present invention. It shouldbe noted that this drawing is purely schematic, for the purpose ofclarifying the different features thereof. In particular, dimensions ofthe different features are not on a common scale.

The apparatus 100 comprises a first main part 101 and a second main part102. In the illustrated preferred embodiment these main parts arearranged with the first main part 101 on top of second main part, withan adjustable spacing 103 between said main parts. When making a surfaceimprint by a process as illustrated in FIGS. 1-6, it may be of greatimportance that the template and the substrate are properly aligned inthe lateral direction, typically called the X-Y plane. This isparticularly important if the imprint is to be made on top of oradjacent to a previously existing pattern in the substrate. However, thespecific problems of alignment, and different ways of overcoming them,are not addressed herein, but may of course be combined with the presentinvention when needed.

The first, upper, main part 101 has a downwards facing surface 104, andthe second, lower, main part 102 has an upwards facing surface 105.Upwards facing surface 105 is, or has a portion that is, substantiallyflat, and which is placed on or forms part of a plate 106 which acts asa support structure for a template or a substrate to be used in animprint process, as will be more thoroughly described in conjunctionwith FIGS. 8 and 9. A heater body 21 is placed on plate 106, or formspart of plate 106. Heater body 21 forms part of a heater device 20, andincludes a heating element 22 and preferably also a cooling element 24,as shown in FIGS. 1-6. Heating element 22 is connected throughconnectors 23 to a energy source 26, e.g. an electrical power supplywith current control means. Furthermore, cooling element 24 is connectedthrough connectors 25 to a cooling source 27, e.g. a cooling fluidreservoir and pump, with control means for controlling flow andtemperature of the cooling fluid.

Means for adjusting spacing 103 are, in the illustrated embodiment,provided by a piston member 107 attached at its outer end to plate 106.Piston member 107 is displaceably linked to a cylinder member 108, whichpreferably is held in fixed relation to first main part 101. As isindicated by the arrow in the drawing, the means for adjusting spacing103 are devised to displace second main part 102 closer to or fartherfrom first main part 101, by means of a movement substantiallyperpendicular to the substantially flat surface 105, i.e. in the Zdirection. Displacement may be achieved manually, but is preferablyassisted by employing either a hydraulic or pneumatic arrangement. Theillustrated embodiment may be varied in a number of ways in thisrespect, for instance by instead attaching plate 106 to a cylindermember about a fixed piston member. It should further be noted that thedisplacement of second main part 102 is mainly employed for loading andunloading the apparatus 100 with a template and a substrate, and forarranging the apparatus in an initial operation position. The movementof second main part 102 is, however, preferably not included in theactual imprint process as such in the illustrated embodiment, as will bedescribed.

First main part 101 comprises a peripheral seal member 108, whichencircles surface 104. Preferably, seal member 108 is an endless sealsuch as an o-ring, but may alternatively be composed of severalinterconnected seal members which together form a continuous seal 108.Seal member 108 is disposed in a recess 109 outwardly of surface 104,and is preferably detachable from said recess. The apparatus furthercomprises a radiation source 110, in the illustrated embodiment disposedin the first main part 101 behind surface 104. Radiation source 110 isconnectable to a radiation source driver 111, which preferably comprisesor is connected to a power source (not shown). Radiation source driver111 may be included in the apparatus 100, or be an external connectablemember. A surface portion 112 of surface 104, disposed adjacent toradiation source 110, is formed in a material which is transparent toradiation of a certain wavelength or wavelength range of radiationsource 110. This way, radiation emitted from radiation source 110 istransmitted towards spacing 103 between first main part 101 and secondmain part 102, through said surface portion 112. Surface portion 112,acting as a window, may be formed in available fused silica, quartz, orglass used for CD/DVD mastering.

In operation, apparatus 100 is further provided with a flexible membrane113, which is substantially flat and engages seal member 108. In apreferred embodiment, seal member 113 is a separate member from sealmember 108, and is only engaged with seal member 108 by applying acounter pressure from surface 105 of plate 106, as will be explained.However, in an alternative embodiment, membrane 113 is attached to sealmember 108, e.g. by means of a cement, or by being an integral part ofseal member 108. Furthermore, in such an alternative embodiment,membrane 113 may be firmly attached to main part 101, whereas seal 108is disposed outwardly of membrane 113. For an embodiment such as the oneillustrated, also membrane 113 is formed in a material which istransparent to radiation of a certain wavelength or wavelength range ofradiation source 110. This way, radiation emitted from radiation source110 is transmitted into spacing 103 through said cavity 115 and itsboundary walls 104 and 113. Examples of usable materials for membrane113, for the embodiment of FIGS. 7-9, include polycarbonate,polypropylene, polyethylene. The thickness of membrane 113 may typicallybe 10-500 μm.

A conduit 114 is formed in first main part 101 for allowing a fluidmedium to pass to a space defined by surface 104, seal member 108 andmembrane 113, which space acts as a cavity 115 for said fluid medium.Conduit 114 is connectable to a pressure source 116, such as a pump,which may be an external or a built in part of apparatus 100. Pressuresource 116 is devised to apply an adjustable pressure, in particular anoverpressure, to a fluid medium contained in said cavity 115. Anembodiment such as the one illustrated is suitable for use with agaseous pressure medium. Preferably, said medium is selected from thegroup containing air, nitrogen, and argon. If instead a liquid medium isused, it is preferred to have the membrane attached to seal member 108.Such a liquid may be a hydraulic oil.

FIG. 8 illustrates the apparatus embodiment of FIG. 7, when being loadedwith a substrate and a template for a lithographic process. For betterunderstanding of this drawing, reference is also made to FIGS. 1-3.Second main part 102 has been displaced downwards from first main part101, for opening up spacing 103. As indicated in FIGS. 1-6, either thetemplate or the substrate are transparent to radiation of a certainwavelength or wavelength range of radiation source 110. The illustratedembodiment of FIG. 8 shows an apparatus loaded with a transparenttemplate 10 on top of a substrate 12. Substrate 12 is placed with abackside thereof on surface 105 of heater body 21, placed on or in thesecond main part 102. Thereby, substrate 12 has its substrate surface 17with the layer 14 of polymerisable fluid facing upwards. For the sake ofsimplicity, all features of heater device 20, as seen in FIGS. 1-6 arenot shown in FIG. 8. Template 10 is placed on or adjacent to substrate12, with its structured surface 11 facing substrate 12. Means foraligning template 10 with substrate 12 may be provided, but are notillustrated in this schematic drawing. Membrane 113 is then placed ontop of template 10. For an embodiment where membrane 113 is attached tothe first main part, the step of actually placing membrane 113 on thetemplate is, of course, dispensed with. In FIG. 8 template 10, substrate12 and membrane 113 are shown completely separated for the sake ofclarity only, whereas in a real situation they would be stacked onsurface 105.

FIG. 9 illustrates an operative position of apparatus 100. Second mainpart 102 has been raised to a position where membrane 113 is clampedbetween seal member 108 and surface 105. In reality, both template 10and substrate 12 are very thin, typically only parts of a millimetre,and the actual bending of membrane 113 as illustrated is minimal. Still,surface 105 may optionally be devised with a raised peripheral portionat the point where it contacts seal member 108 through membrane 113, forcompensating for the combined thickness of template 10 and substrate 12.

Once main parts 101 and 102 are engaged to clamp membrane 113, cavity115 is sealed. Pressure source 116 is then devised to apply anoverpressure to a fluid medium in cavity 115. The pressure in cavity 115is transferred by membrane 113 to template 10, which is pressed towardssubstrate 12 for imprinting the template pattern in the polymerisablefluid layer 14, cf. FIG. 2. For a polymer material of layer 14 havingsufficient viscosity at the operating temperature, typically roomtemperature between 20 and 25° C., imprint may be made directly.However, certain types of polymers need pre-heating to overcome itsglass transition temperature TG, which may be about 60° C. An example ofsuch a polymer is MRL 6000 by Micro Resist Technology. When using suchpolymers, the apparatus 100, having combined radiation and heatingcapabilities, is particularly useful. Heater device 20 is activated toheat polymer layer 14 through substrate 12, by means of heater body 21,until TG has been over come. The pressure of the medium in cavity 115 isthen increased to 5-500 bar, advantageously to 5-200 bar, and preferablyto 5-100 bar. Template 10 and substrate 12 are thereby being pressedtogether with a corresponding pressure. Thanks to flexible membrane 113,an absolutely even distribution of force is obtained over the whole ofthe contact surface between the substrate and the template. The templateand the substrate are thereby made to arrange themselves absolutelyparallel in relation to one another and, the influence of anyirregularities in the surface of the substrate or template beingeliminated.

When template 10 and substrate 12 have been brought together by means ofthe applied fluid medium pressure, radiation source is triggered to emitradiation 19. The radiation is transmitted through surface portion 112,which acts as a window, through cavity 115, membrane 113, and template10. The radiation is partly or completely absorbed in the layer 14 ofpolymerisable fluid, which thereby is solidified in the perfectlyparallel arrangement between template 10 and substrate 12, provided bythe pressure and membrane assisted compression. Radiation exposure timeis dependent on the type and amount of fluid in layer 14, the radiationwavelength combined with the type of fluid, and of the radiation power.The feature of solidifying such a polymerisable fluid is well known assuch, and the relevant combinations of the mentioned parameters arelikewise known to the skilled person. Once the fluid has solidified toform a layer 14′, further exposure has no major effect. However,dependent on the type of polymerisable fluid, post-baking at an elevatedtemperature of 150-160° C. may be necessitated for a time period of0.5-1 hour. With the apparatus 100 according to the present invention,post-baking may be performed in the imprint machine 100, which meansthat it is not necessary to bring the substrate out of the apparatus andinto a separate oven. This saves one process step, which makes both timeand cost savings possible in the imprint process. For the example of MRL6000, post-baking is typically performed at 100-120° C. for about 10minutes. By performing the post-baking step while the template 10 isstill held with the selected pressure towards substrate 10, higheraccuracy in the resulting structure pattern in layer 14 may also beachieved, which makes it possible to produce finer structures. Followingan exposure time and possibly post-baking under compression, dependingon the choice of material and radiation, and dimensions of thepolymerisable layer; the pressure in cavity 115 is reduced and the twomain parts 101 and 102 are separated from one another. In oneembodiment, cooling element 24 of heater device 20 may first be used tocool down the substrate 12 and template 10 before separation. Substrate12 and template 10 are thereafter separated from one another. Afterthis, the substrate is subjected to further treatment according to whatis previously known for imprint lithography.

FIGS. 8 and 9 illustrate a process similar to that of FIGS. 1-3. Again,it should be noted that with a transparent substrate 12, template 10 mayinstead be placed on surface 105 of heater body 21, with substrate ontop of template 10, as shown in FIGS. 4-6.

FIGS. 10-12 illustrates an alternative method of using apparatus 100, inaccordance with an embodiment of the invention. The same referencemarkings are used for like features as in FIGS. 1-3. However, in theprocess of FIGS. 10-12, a transparent template 200 is used, preferablymade from glass or quartz. Template 200 has a structured surface facingsubstrate 12, with projecting pattern-defining protrusions 201 havingopaque layers 202 covering the outer end surfaces of protrusions 201.Preferably, layers 202 are metal layers. In a preferred embodiment,template 200 is manufactured by means of first applying a metal mask 202on selected areas of the template surface, where after an etchingprocess is used for defining grooves between the masked portions.Instead of removing the mask after the etching step, the mask 202 iskept on the template to define the non-transparent outer end surfaces ofthe template protrusions 201. By manufacturing template 200 by means ofthis process, it is also ensured that a near completely even commonplane for the outer end surfaces of protrusions 201 is achieved, sincethe template manufacturing process starts from a flat template body witha plane surface. It should be noted that dimensions illustrated in FIGS.1-12 are exaggerated for the sake of easy understanding. For instance,layers 202 may be only a few atomic monolayers thick.

In FIG. 10, template 200 is pressed into layer 214 on substrate 12,preferably by using an apparatus as described with reference to FIGS.7-9. Layer 214 is in this case a UV-curable negative resist polymer,which may be of any known type. An even pressure is achieved over theentire engaging surfaces of template 200 and substrate 12, thanks to theimprint technique using a membrane and gas pressure as described above.Preferably, the template 200 is pressed into layer 214 such that theouter ends of protrusions 201 come extremely close to substrate layer17, preferably only a few nanometres. In one embodiment, heater device20 is used for pre-heating layer 214 trough substrate 12, in order forthe polymer of layer 214 to overcome the glass transition temperature.

In FIG. 11, radiation 19 is applied through template 200, towardssubstrate 12. Radiation which hits layers 202 is stopped and reflected,and does not reach layer portions 214′. Radiation which radiates betweenprotrusions 201, however, will hit layer 214 and start a curing orsolidification process in layer portions 214″. Preferably, bakingprocess is then performed using heater device 20 for completing thecuring process.

In the step illustrated in FIG. 12, template 200 is separated andremoved from template 12, leaving layer 214 as imprinted. In this shape,substrate 12 is exposed to a negative resist developer fluid. The exacttype of fluid may be of any known kind, although the skilled personrealises that developer type has to be selected dependent on the resistpolymer used. The developer will only remove portions 214′ which werenot exposed to radiation, and which remain only as very thin layers atthe bottom of the recesses in the polymer layer formed by protrusions201. Compared to prior art processes, where an ashing or etching processhas to be applied to remove the remaining polymer portions 214′ in therecesses, which is then also cured, this process is considerably easierand faster. Furthermore, ashing or etching of the patterned polymerlayer 14 will remove material from all parts of layer 214, both portions214′ and 214″, whereas the proposed method only takes away the portions214′ which were not exposed to radiation.

One embodiment of the system according to the invention furthercomprises mechanical clamping means, for clamping together substrate 12and template 10. This is particularly preferred in an embodiment with anexternal alignment system for aligning substrate and template prior topattern transfer; where the aligned stack comprising the template andthe substrate has to be transferred into the imprint apparatus. Thesystem may also contain means for applying a vacuum between template andsubstrate in order to extract air inclusions from the polymerisablelayer of the stacked sandwich prior to hardening of the polymerisablefluid through UV irradiation.

In a preferred embodiment, the template surface 11 is preferably treatedwith an anti-adhesion layer to prevent the cured polymer layer 14′ fromsticking to it after the imprint process. An example of such ananti-adhesion layer comprises a fluorine-containing group, as presentedin WO 03/005124 and invented by one of the inventors of the instantinvention. The contents of WO 03/005124 are also hereby incorporated byreference.

A first mode of the invention, with a transparent template, which hasbeen successfully tested by the inventors, involves a substrate 12 ofsilicon covered by a layer 14 of NIP-K17 with a thickness of 1 μm. Atemplate of glass or fused silica/quartz, with a thickness of 600 μm,has been used. A second mode of the invention, with a transparentsubstrate, which has been successfully tested by the inventors, involvesa substrate 12 of glass or fused silica/quartz covered by a layer 14 ofNIP-K17 with a thickness of 1 μm. A template of e.g. nickel or siliconhas been used, with a thickness of about 600 μm, though any othersuitable non-transparent material can be used.

After compression by means of membrane 113 with a pressure of 5-100 barfor about 30 seconds, radiation source 110 is turned on. Radiationsource 110 is typically devised to emit at least in the ultravioletregion below 400 nm. In a preferred embodiment, an air-cooled xenon lampwith an emission spectrum ranging from 200-1000 nm is employed as theradiation source 110. The preferred xenon type radiation source 110provides a radiation of 1-10 W/cm², and is devised to flash 1-5 μspulses, with a pulse rate of 1-5 pulses per second. In an alternativeembodiment, a continuous mode UV source is used. A window 112 of quartzis formed in surface 104 for passing through radiation. Exposure time ispreferably between 1-30 seconds, for polymerising fluid layer 14 into asolid layer 14′. After successful exposure, second main part 102 islowered to a position similar to that of FIG. 8, following whichtemplate 10 and substrate 12 are removed from the apparatus forseparation and further processing of the substrate.

The disclosed apparatus and method is particularly advantageous forlarge area imprint in a single step, and has as such huge benefits overthe previously known step and flash method. Thanks to themembrane-transferred fluid pressure, the present invention can be usedfor one step imprint of substrates of 8 inch, 12 inch, and even largerdiscs. Even full flat panel displays with sizes of about 400×600 mm andlarger can be patterned with a single imprint and exposure step with thepresent invention. The present invention therefore provides a techniquewhich may for the first time make radiation-assisted polymerisationimprint attractive to large scale production. The invention is usablefor forming patterns in a substrate for production of e.g. printed wireboards or circuit boards, electronic circuits, miniaturised mechanicalor electromechanical structures, magnetic and optical storage media etc.The apparatus according to the invention may of course also be used onlywith the radiation source, or instead only with the heater device.

The invention is defined by the appended claims.

1. Apparatus for transferring a pattern from a template having astructured surface to a substrate carrying a surface layer of aradiation polymerisable fluid, said apparatus comprising a first mainpart and a second main part having opposing surfaces, means foradjusting a spacing between said main parts, support means forsupporting said template and substrate in mutual parallel engagement insaid spacing with said structured surface facing said surface layer, aradiation source devised to emit radiation into said spacing, a cavityhaving a first wall comprising a flexible membrane devised to engagesaid template or substrate, means for applying an adjustableoverpressure to a medium present in said cavity, and a heater devicehaving a surface facing said spacing.
 2. The apparatus as recited inclaim 1, wherein said radiation source is positioned in said first mainpart, devised to emit radiation into said spacing from a firstdirection, and said heater device is positioned in said second mainpart, having said surface of the heater device facing said spacing froma second direction, opposite said first direction.
 3. The apparatus asrecited in claim 1 or 2, wherein said heater device comprises a heatingelement, connected to an energy source.
 4. The apparatus as recited inclaim 3, wherein said heater device comprises a cooling element,connected to a cooling source.
 5. The apparatus as recited in claim 1,wherein said medium comprises a gas.
 6. The apparatus as recited inclaim 5, wherein said medium comprises air.
 7. The apparatus as recitedin claim 1, wherein said means for applying an adjustable overpressureis arranged to adjust the pressure to 1-500 bar.
 8. The apparatus asrecited in claim 1, wherein said cavity is defined by a part of thesurface of said first main part, a flexible seal member arranged in andprotruding from said first main part surface, and said membrane whichengages said seal member.
 9. The apparatus as recited in claim 8,wherein said membrane is disconnectable from said seal member, anddevised to engage said seal member by application of pressure from saidsecond main part.
 10. The apparatus as recited in claim 1, wherein saidmembrane is transparent to a wavelength range of said radiation, saidradiation source being positioned behind said membrane.
 11. Theapparatus as recited in claim 8, wherein said membrane and at least aportion of said surface of said first main part is transparent to awavelength range of said radiation, said radiation source beingpositioned behind said portion of said surface of said first main part.12. The apparatus as recited in claim 8, wherein said portion of saidsurface of said first main part is made from quartz, calcium fluoride orany other pressure stable material being transparent to said radiation.13. The apparatus as recited in claim 1, wherein said radiation sourceis devised to emit radiation at least in a wavelength range of 100-500nm.
 14. The apparatus as recited in claim 10, wherein said radiationsource is devised to emit pulsating radiation with a pulse duration of0.5-10 μs and a pulse rate of 1-10 pulses per second.
 15. The apparatusas recited in claim 1, wherein said membrane is made from a polymermaterial.
 16. The apparatus as recited in claim 1, wherein said membranehas a diameter or width of 50-1000 mm.
 17. The apparatus as recited inclaim 1, where said substrate acts as said membrane. 18-33. (canceled)